Method for making spherical crystals

ABSTRACT

The present invention relates to a method for forming crystal substrates on which can be easily formed spherical crystals which have superior crystal structure and little defect in shape. The present invention also relates to a method for making crystal substrates on which can be easily formed spherical crystals which have little defect in shape and from which impurities have been removed. Projections are formed integrally from a semiconductor crystal base, and flow regulating film is formed to cover the entire outer surface of the crystal base and a base portion of the projections. A heating beam is applied to the tips of the projections, and the end portions of the projections are melted. The surface tension of the melt and the melt regulation by the flow regulating film act to solidify the melt in a spherical shape, thus forming a spherical crystal.

BACKGROUND OF THE INVENTION

The present invention relates to a method for making spherical crystals.In particular, the present invention relates to a method for makingspherical crystals for use in semiconductors, dielectrics, magneticbodies, and superconductors.

Spherical crystals can be made by growing crystals in a spherical formusing the surface tension of a melt. Because of the symmetry in theouter shape due to the spherical structure, these spherical crystalsallow easy creation of single crystals which have few defects and nodisorder in atomic arrangement inside the crystals. In particular, anenvironment affected minimally by gravity will permit single crystalsthat are determined by the surface tension of the melt and are morespherical. Furthermore, since buoyancy does not affect the process,there is no thermal convection due to temperature differences, thuspreventing disturbances. In cases where two or more elements are used togrow a crystal, segregation due to different specific gravities in theelements are avoided. Thus, it is possible to make spherical singlecrystals that have uniform composition and good crystallinity. Thesetypes of high-quality spherical crystals have many possibilities inindustrial fields that use crystals. These spherical crystals can beused directly in applications such as electronic devices, opticalelements, and functional elements.

Conventionally, single crystals for semiconductors and the like havebeen formed in the shape of rods, plates and films. Thus, the crystalshave not been grown as spheres from the start. In particular, there havebeen no proposals at all for technologies that allow localized growth ofspherical crystals on plate-shaped or rod-shaped crystal bases.

There have been three types of technology to grow single crystals forsemiconductors: the method of using a melt to grow crystals; the methodof growing crystals from a solute using a solvent; and the method ofgrowing crystals through chemical deposition from the gas phase.

Generally, in the method of using a melt to grow crystals, the entirematerial is stored in a container such as a crucible or an ampoule. Thematerial is heated and melted in an electric furnace that useshigh-frequency heating or resistance heating. A seed crystal is put incontact with the melt, and it is pulled up while being rotated (the CZmethod).

In the floating zone method (FZ method), a crucible is not used. Thismethod is another popular method for growing single crystals. In thismethod for growing crystals, the melt forms melt zones between arod-shaped seed crystal and a polycrystal. The melt is supported bysurface tension while moving toward the polycrystals and are transformedinto single crystals. However, forming stable floating zones in thismethod requires high surface tension and the use of material with lowdensity.

In another method for growing single crystals, an electric furnace isnot used, and instead a laser beam is used as a heat source. A materialwith a high melting point such as Spinel (MgAl₂ O₄) is melted, and theresulting melt is used to grow single crystals. Film crystals areobtained by melting amorphous silicon films on a silicon wafer. Thesetechniques are well known. However, there is still no known method todirectly create spherical single crystals by using heating beams such aslaser beams to melt materials such as semiconductors, dielectrics,magnetic bodies, superconductors or metals.

There have been attempts made to grow semiconductor crystals and certainalloy crystals in microgravity environments. It has also been known thatin microgravity conditions, melts have accidentally leaked to formspherical crystals. However, there have been no proposals for methods tointentionally grow spherical crystals. Furthermore, the idea of makingspherical crystals by growing crystals spherically from a melt has notbeen proposed at all. The inventor of the present invention is focussingon the various possibilities for applying spherical crystals toelectronic devices and optical elements. However, the making ofspherical crystals using the conventional technology requires mechanicalpolishing of the crystal body, chemical etching and the like.

In the method for growing crystals by placing material in a containersuch as a crucible, melting it, and solidifying it, it is possible forthe molten material and the material of the container to react. Thiscauses impurities from the container to dissolve and makes it difficultto grow high-quality crystals. Furthermore, when the material solidifiesinside the container, it was possible for heterogeneous nuclei to becreated due to contact with the container wall, and there could beinternal warping within the crystals due to uneven cooling conditions.Thus, it was extremely difficult to grow crystals without defects.Furthermore, according to this conventional method, the objective is toperform bulk production by placing the material in the container,melting it and solidifying it. Therefore it is impossible to freely growspherical single crystals at a prescribed position at a restricted sizeor amount. For example, it would be completely impossible to growspherical crystals for electronic devices or optical elements on asection of a crystal base. In the conventional method for forming singlecrystals by melting material in bulk and solidifying from one end of aseed crystal, the resulting crystals would be rod-shaped orplate-shaped. These shapes do not have three-dimensional symmetry asspheres do, and so they tended to result in defects due to factors suchas disorder in the atomic configuration within the crystals, or thermalwarping.

It may be possible to grow spherical single crystals by melting andsolidifying the material in zero-gravity or microgravity. However, theheating, melting and solidifying takes a long time in the conventionalmethod because heating methods such as electric furnaces and infraredlamps are used. These could not be used in the drop-shaft type or thedrop tower type facilities for microgravity experiment, which wouldrequire crystals to be grown within a very short time span of 10 secondsor less. This would restrict this method to microgravity in space, whichwould make the growth of spherical crystals extremely costly.

The present applicant has conducted various experiments to establish amethod for making spherical crystals. In a past application, Japanesepatent application 5-284499, the present applicant proposed such amethod for making spherical crystals. Referring to FIG. 24(a), a thinprojection 101 comprising a crystal made from a metal or a metal oxideor a non-metallic material. Projection 101 is disposed so that itprojects from the surface of a crystal base 100, comprising a metal or ametal oxide or a non-metallic material. Referring to FIG. 24(b) and FIG.24(c), at least a portion of projection 101 is heated with a heatingbeam 102, so that surface tension causes a spherical crystal tosolidify.

Referring to FIG. 24(c), because projection 101 and melt 103 are madefrom the same material and thus have high wettability, melt 103 flowsalong the surface of the unmelted portion of projection 101a. Melt 103solidifies in a thin and elongated shape, and does not result in aspherical shape. Thus, it became clear that a spherical crystal having aroughly spherical shape could not be formed. In particular, the specificgravity of the melt (volume x density x acceleration of gravity) islarge, facilitating the Marangoni effect, tending to cause the crystalstructure to fall apart.

If a laser beam is used as the heating means, the cooling due to heatconduction is quick, allowing solidification in a short time. Thisminimizes the collapse of the spherical shape. If an infra-red beam isused for heating, the radiation energy density will be relatively lowand the rate of temperature increase will be slow. This increases thetendency of the melt to flow along the unmelted portion of theprojection, thus facilitating the collapse of the crystal shape.

When the above crystal structure solidifies, solidification(crystallization) begins from the unmelted portion of the projection. Ifthe crystal used in the projection is an inexpensive crystal that doesnot have a high degree of purity, the impurities in the crystal wouldaccumulate at the surface of the spherical crystal. Thus, it would bedifficult to form a spherical crystal having a high degree of purity.

OBJECTS AND SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for easilyforming a spherical crystal on a crystal base that has a superiorcrystal structure without any collapse of shape and that has no internalstress or crystal defects. A further object of the present invention isto provide a method for easily forming a high quality spherical crystalon a crystal base without any collapse of shape and that has fewimpurities and defects within the crystal.

The present invention (claim 1) is a method for making sphericalcrystals and includes: a first process wherein a thin projectioncomprising a crystal made from metal or a metal oxide or a non-metallicmaterial is disposed so that it projects from a surface of a crystalbase comprising a metal, a metal oxide or a non-metallic material; asecond process wherein a flow regulating film having a higher meltingpoint than the crystal making up the projection is formed over an entireouter surface of a base portion of the projection, away from a tip ofthe projection; a third process wherein a heating beam is applied to thetip of the projection to melt the portion of the projection more towardthe tip than the flow regulating film; a fourth process wherein theapplication of the heating beam to the projection is stopped and aspherical crystal having a roughly spherical shape is solidified throughthe surface tension of the molten portion and the flow regulating actionof the flow regulating film. In this invention, the projection can bemade from the same crystal as the crystal base and formed integrallywith the crystal base, or a projection made from a crystal identical toor different from the crystal base can be fixed to the surface of thecrystal base.

In the first process, it would also be possible to have a thinprojection formed so that it projects integrally from a semiconductorcrystal base (claim 2). It would also be possible to dispose a thinprojection comprising a semiconductor crystal so that it projects fromthe surface of a semiconductor crystal base (claim 3).

Referring to FIG. 1(a) and FIG. 2(a), the present invention involvesdisposing a thin projection 11 comprising a crystal made from a metal ora metal oxide or non-metallic material so that it projects from thesurface of a crystal base 10 comprising a metal or a metal oxide or anon-metallic material. Referring to FIG. 1(b) and FIG. 2(b), a flowregulating film 12 is formed over the entire outer surface of a baseportion 11 of projection 11, located from the tip. Referring to FIG.1(c) and FIG. 2(c), a heating beam 13 is applied to the tip ofprojection 11 so that the portion of projection 11 past flow regulatingfilm 12 is melted. Referring to FIG. 1(d) and FIG. 2(d), the applicationof heating beam 13 on projection 11 is halted, and a molten portion 11bis solidified into a spherical crystal 14 that is roughly spherical inshape through the effect of surface tension and through the flowregulating operation of flow regulating film 12.

For the metallic material described above, single metals or varioustypes of alloy metals can be used. In particular, various types ofsemiconductors, dielectrics, magnetic material, superconductors and thelike can be used.

The projection described above, comprising crystals made from metals ormetal oxides or non-metallic material, is made up of single crystals orpolycrystals. The heating beam can be a heating beam having a highenergy density, such as lasers, condensed infra-red beams, and electronbeams.

When a laser is to be used for the heating beam described above, thelaser beam can be made to have a high energy density and a very smallfocus diameter. Thus, a laser beam is particularly suited for meltingthe projection, which has a very small thickness on the order of betweentens of microns and hundreds of microns. By forming multiple rows ofprojections and scanning a laser beam over the tips of the arrangedprojections, it is possible to perform the third and fourth processes ina very short period of time. In particular, the method can be used formaking spherical crystals in free-falls microgravity experimentalfacilities or in airplanes flying in a parabolic path. This is extremelyuseful in reducing the costs involved in microgravity crystal growth.

Also, when a laser is used, there is almost no heating in the areasother than the portion to be melted, making it possible to heat and meltonly the intended portions. It is also possible to adjust the amount ofheat entry appropriately by adjusting the laser beam output and the scanspeed. Heating can also be performed efficiently for specific areas asdesired, such as a portion of the projection or the entire projection.When necessary, different elements can be attached to the tip of theprojection for doping or for forming mixed crystals. The differentelement would be melted together with the projection to solidify into aspherical crystal.

The flow regulating film described above is a film having a meltingpoint that is higher than that of the crystal making up the projection.Various types of metal oxides, metal nitride and the like can be usedfor the film. However, it would be desirable to make the flow regulatingfilm out of a material that has a high melting point and low wettabilityrelative to the material used in the projection, since the film servesto restrict the flow of the molten portion of the projection along thesurface of the unmelted portion of the projection. The formation of theflow regulating film can be performed, for example, by using chemicalvapor deposition (CVD) or the like to form a film having a high meltingpoint over the entire surface of the crystal base and the projection.Then, etching or the like would be used to eliminate the film for allareas except for the base portion of the projection. Referring to FIG. 1and FIG. 2, there are shown examples where flow regulating films arealso formed over the crystal base, but it is acceptable to omit the flowregulating film for the surface of the crystal base.

Since surface tension and regulation of flow by the flow regulating filmare used to solidify a spherical crystal in a roughly spherical shape,it is necessary for the projection to be thin enough that the effects ofsurface tension are dominant. The thickness of the projection can be,for example, a few mm or less, and can be a few hundred microns insemiconductors and the like. The cross-section shape of the projectionis not limited to a circular shape, and can also be rectangular, squareor the like. By applying a heating beam for a short period orinstantaneously, it is possible to melt the projection at the portionpast the flow regulating film.

Due to surface tension in the melt and the flow regulating action by theflow regulating film, the portion that is melted by the heating beamforms a roughly spherical shape without any collapse in shape, and itssurface forms a free surface. When the application of the heating beamis halted, the molten portion of the projection forms a sphericalcrystal by solidifying rapidly while maintaining the spherical shape.The solidification occurs mainly due to the heat absorption into thecrystal base via the projection. The crystal grows with a directionalitycentering on the portion of the seed crystal that is not molten and thatis in contact with the melt. Since the nucleus of the crystal growth isat the borderline between solid phase and liquid phase, and since theoutward flow of latent heat in solidification occurs rapidly on the seedcrystal side, the growth from the seed crystal to the crystal proceedsquickly. Then, as growth proceeds from the seed crystal to the crystal,the crystal growth proceeds at the central portion of the sphericalportion before the outer perimeter portion of the spherical portion sothat the single crystal grows and solidifies from the center of thesphere toward the outer perimeter. In particular, it is possible tolimit the heat dissipation from the outer perimeter of the melt bysetting a high atmosphere temperature as appropriate. Because crystalgrowth proceeds from the center of the sphere outward, and because thetemperature gradient in the direction of crystal growth is steep,disturbances in the crystal growth surface due to constitutionalsupercooling and the like are avoided, and internal stress and crystaldefects in the spherical crystal do not tend to occur.

Solidification occurs while a roughly spherical shape is maintained bythe surface tension of the molten portion and the melt regulation by theflow regulating film. Because of the symmetry of the sphere surface andthe spherical symmetry of the growth of the crystal, the internalstructure of the spherical crystal maintains a spherical symmetry aswell. There tends to be little disorder in the atomic arrangement, andthe surface of the spherical crystal forms a crystal surface having aconstant mirror indices. The resulting single crystal is an idealcrystal with almost no defects. In particular, the damage and the strainresulting from mechanical or chemical processing do not occur, and thesurface of the spherical crystal forms an ideal spherical mirror.However, if an impurity is contained in the projection, the impuritywill be segregated at the surface of the spherical crystal.

As described above, spherical crystals made from single crystals orroughly single crystals can be formed very easily on a crystal base byusing a heating beam to melt and then solidifying the melt. Inparticular, it is possible to form spherical crystals in a manner thatis significantly easier and more inexpensive compared to makingspherical crystals by mechanically or chemically processingsemiconductors.

The surface of the spherical crystal described above forms an idealspherical mirror, and will not have the defects that tend to occur onthe surface of crystals. Furthermore, thermal stress, as occurs insemiconductor wafers, is avoided since the inducement of surface stressdue to non-uniform differences in thermal expansion of the oxide filmdoes not tend to occur.

Furthermore, when at least a portion of a projection is to be melted andcrystallized, the melt comes into contact with only the crystals of theprojection, which serve as the seed crystal, and the flow regulatingfilm. Thus, high-quality spherical crystals are possible, and theproblems that occur when crystals are grown while held in a containersuch as a crucible are avoided. These include: the mixture of outsideimpurities; pollycrystallization due to thermal convection or irregulargrowth of nuclei caused by non-uniform heat absorption into thecontainer; and crystal deformations due to thermal stress between thecontainer and the growing crystals. Also, the melt is crystallized whileit absorbs heat from the seed crystal. Thus, crystal growth proceedsrapidly while the growth nucleus is restricted by the seed crystal. Thismakes it difficult for constitional supercooling to take place, andprovides a high-quality spherical crystal. Furthermore, sincecrystallization is performed while a roughly spherical shape ismaintained through surface tension of the melt and flow regulation bythe flow regulating film, it is possible to form a spherical crystalhaving a fixed shape.

On a final note, when a semiconductor single crystal such as silicon isused for the projection, it is possible to form a sphericalsemiconductor single crystal. The use of a dielectric projection makesit possible to form a dielectric spherical crystal. The use of amagnetic material for the projection makes it possible to form amagnetic spherical crystal. The use of a superconductor projection makesit possible to form a superconductor spherical crystal.

Referring to FIG. 1, when a projection is formed integrally with asemiconductor crystal base, it is possible to form a semiconductorsingle crystal or roughly single crystal at the tip of the base portionof the projection formed integrally with the semiconductor crystal base.Referring to FIG. 2, it is possible to form a semiconductor singlecrystal or roughly single crystal spherical crystal in the followingmanner. A thin projection comprising a semiconductor crystal is adheredor bonded to the surface of a semiconductor crystal base so that itprojects. An example of this would be the adhesion of a semiconductorcrystal having a prescribed thickness to the entire surface of thecrystal base, and then the semiconductor crystal is processed so that aplurality of projections are formed in a matrix formation. Thesemiconductor crystal base can be a single crystal base or a polycrystalbase that is not a single crystal. Because the projection comprises asemiconductor crystal, it is possible to form a semiconductor singlecrystal or roughly single crystal spherical crystal.

The present invention (claim 4) is a method for making sphericalcrystals including: a first process wherein a thin projection made froma crystal comprising a metal or a metal oxide or a non-metallic materialis disposed so that it projects from the surface of a crystal basecomprising a metal or a metal oxide or a non-metal material; a secondprocess wherein a flow regulating film having a melting point higherthan that of the crystal used in the projection is formed on the surfaceof the crystal base from which the projection projects; a third processwherein a heating beam is applied to the tip of the projection and theentire projection is melted; and a fourth process wherein theapplication of the heating beam to the projection is halted and themolten portion is solidified into a spherical crystal having a roughlyspherical shape due to surface tension and flow regulation by the flowregulating film. It would also be possible to form a projectioncomprising the same crystal as used in the crystal base integrally withthe crystal base. Or, it would also be possible to fix a crystal that isthe same as or different from the crystal base to the surface of thecrystal base.

In the first process, it would also be possible to form a thinprojection projecting integrally from the surface of a semiconductorcrystal base (claim 5). It would also be possible to dispose a thinprojection comprising a semiconductor crystal so that it projects fromthe surface of a semiconductor crystal base (claim 6).

Referring to FIG. 3(a) and FIG. 4(a), in the present invention a thinprojection 21 comprising a metal or a metal oxide or a non-metalliccrystal is disposed so that it projects from a surface of a crystal base20 comprising a metal or a metal oxide or a non-metal material.Referring to FIG. 3(b) and FIG. 4(b), a flow regulating film 22 having amelting point higher than that of the crystal used in projection 21 isformed on the surface of crystal base 20 from which the projectionprojects.

Referring to FIG. 3(c) and FIG. 4(c), a heating beam 23 is applied tothe tip of projection 11, and projection 21 is melted entirely.Referring to FIG. 3(d) and FIG. 4(d), the application of heating beam 23to projection 21 is halted. A spherical crystal 24 having a roughlyspherical shape is solidified from a molten portion 21b described abovedue to surface tension and flow regulation by flow regulating film 22.In the present invention, it is possible to form spherical crystalssimilar to the ones described above on the surface of a crystal base.

Referring to FIG. 3, if a thin projection is formed so that it projectsintegrally from the surface of a semiconductor crystal base, it ispossible to form spherical semiconductor single crystals or roughlysingle crystals on the surface of a semiconductor crystal base. As inthe spherical crystals described above, these spherical crystals havealmost no internal stress and have an internal structure that isspherically symmetrical. There is no disorder in the atomic arrangement,and the result is an ideal crystal with almost no crystal defects andwith a spherical crystal surface having a constant mirror indices.

Referring to FIG. 4, there is shown the example of a thin projectioncomprising a semiconductor crystal that is adhered or bonded so that itprojects from the surface of a semiconductor crystal base. In this case,the semiconductor crystal base can be a single crystal base, or it canbe a polycrystal base that is not a single crystal. As described above,since the projection comprises a semiconductor crystal, a semiconductorspherical single crystal or roughly-single crystal can be grown.

It is possible to use a metallurgical-grade semiconductor base that doesnot have a high degree of purity for the semiconductor crystal base orthe projection (claim 7). In this case it is possible to significantlyreduce material costs for the crystal base or the projection. However,if the crystal base and the projection are formed integrally, asemiconductor spherical crystal that does not have a high degree ofpurity will result. But as noted below, it is possible to eliminateimpurities within the spherical crystal, so this is not a major obstaclein implementation.

It is possible to use a semiconductor single crystal base as thesemiconductor crystal base (claim 8). Integrally forming the projectionwith the crystal base will result in the crystal used in the projectionalso being a semiconductor single crystal, thus making it possible toform spherical crystals that are semiconductor single crystals.

It is possible to form spherical crystals comprising semiconductorsingle crystals by using a semiconductor single crystal in a projectionthat is not integral with a semiconductor crystal base (claim 9).

In cases where at least the fourth process is performed in zero-gravityor microgravity environments (claim 10), there is little effect fromgravity on the molten portion. Surface tension and flow regulation dueto the flow regulating film results in the formation of sphericalcrystals with almost perfectly spherical shapes. Also, since thermalconvections due to gravity can be ignored, spherical crystals withimproved quality are possible. Furthermore, multiple types of materialhaving different specific gravity can be used to form spherical crystalsthat are mixed-crystals or compounds. In this case, the differences inspecific gravity do not cause separation, sedimentation, or buoyancy, itis possible to grow single crystals with a uniform composition.

When a spherical crystal solidifies, crystal growth occurs from theunmelted crystal (the crystal making up the projection or the crystalmaking up the crystal base) and solidification occurs from the center ofthe spherical melt toward the surface. The impurities accumulate on thesurface of the spherical crystal due to segregation. After the fourthprocess, it would be possible to perform a fifth process wherein thesurface of the solidified spherical crystal is etched in order toeliminate the impurities accumulated on the surface of the sphericalcrystal (claim 11).

It would also be possible to repeatedly perform the fifth process,wherein impurities accumulated on the surface of the solidifiedspherical crystal are eliminated by etching the surface of the sphericalcrystal, and a sixth process, wherein the spherical crystal for whichthe impurities were eliminated in the fifth process is then melted againand solidified in a spherical shape, thereby recrystallizing thecrystal. By increasing the number of times this is repeated, it ispossible to increase the purity of the spherical crystal. Because thespherical crystal can be made more pure in this manner, it is possibleto make the projection out of very inexpensive crystals that do not havea high degree of purity. This is especially advantageous when theprojection and the crystal base are formed integrally, since a veryinexpensive crystal that does not have a high degree of purity can beused for the crystal base.

It is also possible to eliminate the internal stress and lattice defectsin the solidified crystal when annealing is performed on the sphericalcrystal (claim 13). This can improve the properties of the sphericalcrystal.

It is also possible to form a new oxide film on the surface of thesolidified spherical crystal after the old oxide film on the surface ofthe spherical crystal is eliminated. Then, heat would be applied to thespherical crystal so that impurities within the spherical crystal wouldbe gettered by the oxide film (claim 14). Elements with highcoefficients of diffusion (such as Au, Ag, Cu in silicon crystals) havethe property of being gettered into the oxide film when heat treatmentis applied to accelerate diffusion. Thus, with the methods describedabove, it is possible to improve the purity of the spherical crystal andimprove the electro and optical properties.

It is also possible to form a new oxide film on the surface of thesolidified spherical crystal after the old oxide film on the surface ofthe spherical crystal is eliminated, and then to apply heat to thespherical crystal so that the impurities within the spherical crystalare gettered into the oxide film (claim 15). Because elements havinghigh coefficients of diffusion as described above cannot always becompletely eliminated, the elements having high coefficients ofdiffusion are eliminated in the same manner as described in claim 14.This improves the purity of the spherical crystal.

The above, and other objects, features and advantages of the presentinvention will become apparent from the following description read inconjunction with the accompanying drawings, in which like referencenumerals designate the same elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a)-(d) are drawings for the purpose of explaining the conceptsinvolved in the four processes used to integrally form a crystal baseand a projection and then to form a spherical crystal out of a portionof the projection.

FIGS. 2(a)-(d) are drawings for the purpose of describing the conceptsinvolved in the four processes used to fix a projection to a crystalbase and then to form a spherical crystal out of a portion of theprojection.

FIGS. 3(a)-(d) are drawings for the purpose of describing the conceptsinvolved in the four processes used to integrally form a crystal baseand a projection and then to form a spherical crystal out of the entireprojection.

FIGS. 4(a)-(d) are drawings for the purpose of describing the conceptsinvolved in the four processes used to integrally fix a projection to acrystal base and then to form a spherical crystal out of the entireprojection.

FIG. 5 is a plan drawing of a crystal base and a projection relating toembodiment 1 of the present invention.

FIG. 6 is a cross-section drawing along the VI--VI line in FIG. 5.

FIG. 7 is a drawing corresponding to the drawing in FIG. 6 where asilicon oxide film is formed.

FIG. 8 is a drawing corresponding to the drawing in FIG. 6 where a flowregulating film is formed.

FIG. 9 is a plan drawing of a spherical crystal array containing 25spherical crystals.

FIG. 10 is a cross-section drawing along the X--X line in FIG. 9.

FIG. 11 is a plan drawing of the crystal base and the projectionrelating to embodiment 2 of the present invention.

FIG. 12 is a cross-section drawing of the crystal base, the projectionand the silicon oxide film in FIG. 11.

FIG. 13 is a plan drawing of the crystal base, the projection and theflow regulating film in FIG. 11.

FIG. 14 is a cross-section drawing along the XIV--XIV line in FIG. 13.

FIG. 15 is a plan drawing of the spherical crystal array formed on acrystal base shown in FIG. 11.

FIG. 16 is a cross-section drawing along the XVI--XVI line in FIG. 15.

FIG. 17 is a cross-section drawing of the crystal base, the projectionand the flow regulating film relating to embodiment 3.

FIG. 18 is a cross-section drawing of the crystal base relating toembodiment 8.

FIG. 19 is a cross-section drawing of the crystal base and theprojection in FIG. 18.

FIG. 20 is a cross-section drawing of the crystal base, the projectionand the flow-regulating film relating to embodiment 9.

FIG. 21 is a cross-section drawing of a spherical crystal array formedon the crystal base in FIG. 20.

FIG. 22 is a plan drawing of the projection and the crystal baserelating to an alternative embodiment.

FIG. 23 is a plan drawing of the crystal base and the spherical crystalmade from the configuration in FIG. 22.

FIG. 24(a) is a cross-section drawing of the crystal base and theprojection relating to the prior art. FIG. 24(b) is a cross-sectiondrawing of the crystal base and the spherical melt. FIG. 24(c) is across-section drawing of the crystal base and the spherical melt.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, the following is a description of theembodiments of the present invention.

Embodiment 1

First, in the first process, a crystal substrate 30 (corresponding tothe crystal base) is prepared. Crystal substrate 30 is a square platecomprising silicon single crystals, has a thickness of 2.0 mm and itsmain surface has a crystal orientation index of (111).

Referring to FIG. 5 and FIG. 6, in the second process, six sets ofgrooves 31 are formed with a diamond multi-blade saw along the X axisand the Y axis of crystal substrate 30. Each groove 31 has a depth of1.0 mm and a width of 0.5 mm. As a result, square, pillar-shapedprojections 32 comprising silicon single crystals form a 5-by-5 matrixon crystal substrate 30, excluding the outer rim areas. Each projection32 has a tip surface of 0.25 mm-by-0.25 mm, and a height of 1.0 mm. Eachprojection 32 is connected integrally at its base with crystal substrate30, made from the original silicon single crystals.

The surfaces processed with the saw as described above have someprocess-induced defect layers. In order to eliminate theseprocessing-altered layers, in the third process light etching isperformed on the side of crystal substrate 30 having projections 32.This is a known technique. In this case, etching is performed with anetchant comprising a mixed acid made from hydrofluoric acid and nitricacid diluted in water.

Next, in the fourth process, crystal substrate 30, on which areprojections 32, is placed in a thermal oxidation furnace and oxidizedfor a prescribed amount of time in a temperature of about 1000 degreesC. Referring to FIG. 7, a silicon dioxide film 33, comprising SiO₂having a thickness of 0.5-1.0 microns, is formed over the entire surfaceof crystal substrate 30, to which projections 32 are attached. Thissilicon dioxide film 33 has a higher melting point than silicon singlecrystals. It tends not to react chemically with molten silicon and alsohas a low wettability relative to molten silicon.

Silicon dioxide film 33 does not need to be formed over the entiresurface of crystal substrate 30, and need only be formed at least on theentire surface of projections 32.

Tip portions 32b comprise everything past bases 32a (approximately 0.2mm in length), located 0.8 mm from the tips of projections 32. Referringto FIG. 8, in the fifth process, silicon dioxide film 33 is eliminatedfrom the entire surface of tip portions 32b (approximately 0.8 mm inlength). As a result, flow regulating films 33a, which are made fromsilicon dioxide film 33, are formed over the entire outer surface ofbases 32b of projections 32. When a portion of silicon dioxide film 33is to be eliminated, a photo-resist approximately 0.2 mm in thickness isapplied to the bottoms of grooves 31 of crystal substrate 30. Silicondioxide film 33 is then eliminated by etching with diluted hydrofluoricacid or the like.

When tip portions 32b of projections 32 are melted in the next process,flow regulating films 33a serve to regulate the flow of the siliconsingle crystal melt along the surface of bases 32a of projections 32.

Next, for the sixth process, a carbon dioxide laser that produces alaser beam is prepared. The laser beam serves as a heating beam formelting tip portions 32b of the plurality of projections 32 formed oncrystal substrate 30. The oscillating frequency of the laser beam fromthis carbon dioxide laser device is 10.6 microns, the output of thecarbon dioxide laser device is 30 watts, and the pulse-repetitionfrequency is 5 kHz. A focusing lens is used so that the beam diameter ofthe laser beam is approximately 0.1 mm. The atmosphere in which thelaser is applied is air, and resistive heating is performed beforeapplication of the laser to preheat crystal substrate 30 toapproximately 127 degrees C.

Next, in the seventh process, crystal substrate 30, on which projections32 are attached, is attached to a carrier so that tip surfaces 32c ofprojections 32 are pointed downward. The carrier can movetwo-dimensionally, in the X and Y directions. Crystal substrate 30 ismoved in the X direction at a speed of 0.5 mm/sec so that the laser beamis scanned along the X direction over a row of five tip surfaces 32c onprojections 32. The carrier is then moved by one pitch in the Ydirection, and the scan is repeated. Thus, a laser beam is scanned insequence perpendicularly over tip surfaces 32c of projections 32 foreach of the rows. When the laser beam is applied, tip portion 32b ofprojection 32 on which the laser is applied melts instantaneously. Themolten melt increases in volume and grows in a spherical shape. Aspherical shape is maintained because of surface tension and the flowregulating activity of flow regulating film 33a. When application of thelaser stops, the melt solidifies instantaneously into a sphericalcrystal 34 comprising the same silicon single crystal as projection 32.Referring to FIG. 9 and FIG. 10, spherical crystal 34 grows integrallyat the end of base 32a of projection 32, which serves as the seedcrystal. Spherical crystal 34 has a diameter of approximately 0.45 mmand the surface is spherical with a smooth luster.

Referring to FIG. 9 and FIG. 10, in this manner 25 spherical crystals 34comprising silicon single crystals are made in an extremely short periodof time. The theory behind how spherical crystals 34 form idealspherical silicon single crystals is described in claim 1 as well as inthe advantages of the invention, so this will be omitted here to preventoverlapping.

Spherical crystal array 34A, made as described above, comprises: acrystal substrate 30 comprising silicon single crystals; a plurality ofbases 32a (bases 32a of projections 32) comprising silicon singlecrystals and arranged to form a 5-by-5 matrix; and spherical crystals 34roughly spherical in shape, formed integrally at the tips of theplurality of bases 32a and comprising silicon single crystals. Afterthis spherical crystal array 34A is made, it can be applied to variouselectronic devices, optical elements, functional elements, and the like.This can be done by introducing impurities for doping on the surfaces ofeach of the plurality of spherical crystals 34, growing thin crystallayers using vapor phase deposition technique or the like, formingintegrated circuits, with connecting electrodes and thin metallic wires.

Furthermore, spherical crystals 34 can be cut away from crystalsubstrate 30 so that they can be used as new electronic devices, opticalelements or functional elements that are spherical in shape.

In particular, spherical crystal arrays can be effective forlight-emitting diodes that can emit light in the same manner in anydirection. Also, they are effective for photo-diodes and solar cells,since they can absorb light from any direction and they have a largesurface area.

Also, by disposing a common electrode on crystal substrate 30, thewiring structure for the spherical crystals can be simplified.

Embodiment 2

(see FIG. 11-FIG. 16)

In this embodiment, the only difference with embodiment 1 is the factthat projections 32A are formed in a cylindrical shape rather than asquare column shape. Therefore, elements that have identical functionsas those in embodiment 1 above are given identical or similar numeralsand the descriptions are omitted.

First, the first process is performed as in embodiment 1. Referring toFIG. 11, in the second process, ultrasonic processing is used to formcylindrical projections 32A in a 5-by-5 matrix on the surface of crystalsubstrate 30, which has a thickness of approximately 2.0 mm andcomprises silicon single crystals. In this case, a slurry containing SiCor Al₂ O₃ powder (polishing powder) is fed to the end of a DI horn whileit vibrates ultrasonically. The DI horn is pressed against the surfaceof crystal substrate 30, and the substrate is processed to formcylinders in the same shape as the DI horn due to the impact of thepolishing powder. The dimensions of projections 32A can be, for example,0.15 mm diameter and 1.0 mm height.

The cylindrical projections 32A have more symmetry than the squarecolumn shaped projections 32 in embodiment 1. This provides superiorspherical symmetry in spherical crystals 34A.

Embodiment 3

(see FIG. 17)

The first process through the fifth process in embodiment 3 areidentical to the first process through the fifth process in embodiment1, so their descriptions will be omitted here.

Referring to FIG. 17, in the sixth process following the fifth process,germanium films 35 are formed on tip surfaces 32c of projections 32 byvacuum evaporating for silicon and germanium mixed crystal formation ata thickness of approximately 1.0 microns on the tip surfaces of the 25projections 32 on crystal substrate 30.

One way to form germanium films 35 is to apply a photo resist over thesurface of crystal substrate 30 excluding the areas where germaniumfilms 35 are to be formed. Then, germanium would be vacuum-evaporatedand the photo resist would be eliminated.

A seventh process, identical to the sixth process in embodiment 1, isthen performed and spherical crystals comprising mixed single crystalsof silicon and germanium are formed. However, a hydrogen gas atmosphereis used rather than air for heating, melting and solidification.Elements identical to elements in embodiment 1 are given identicalnumbers and the descriptions are omitted. The theory behind how thesespherical crystals are ideal spherical crystals is described in theexplanation of claim 1, and they will be omitted here to avoid overlap.

The mixed single crystals of silicon and germanium have an energy gap inthe forbidden band that is smaller than that of silicon and larger thanthat of germanium. These crystals have properties that can be used inthe production of photo diodes and high-speed transistors built inheterojunctions.

The spherical crystal array formed on a crystal substrate as describedabove comprises: a crystal substrate 30 comprising silicon singlecrystals; a plurality of bases 32a (bases 32a of projections 32)comprising silicon single crystals and arranged in a 5-by-5 matrix oncrystal substrate 30; and spherical crystals roughly spherical in shapeformed integrally on the ends of each of the plurality of bases 32a andcomprising single crystals of silicon-germanium mixed crystals.

In this embodiment 3, the spherical crystals are formed as singlecrystals of silicon-germanium mixed crystals. However, it would also bepossible to substitute the germanium film 35 described above with a filmof phosphorous, arsenic, antimony or the like to serve as an impurityfor doping (an impurity as a donor). Alternatively, a film of boron,aluminum, gallium, indium or the like can be formed as an impurity fordoping (an impurity as an acceptor). In these cases, the sphericalcrystals can form type n- or type p- semiconductor single crystals.Instead of in the form of films, it is possible to introduce theseimpurities for doping into spherical crystals through using chemicalvapor deposition in the gas phase or using impurity diffusion in the gasphase.

Furthermore, it is possible to stack type n- and type p- semiconductorsingle crystal layers on the surface of spherical crystals made fromtype n- or type p- semiconductor single crystals. This can be done byforming an oxide film and etching, vapor phase growth and the like. Byforming electrodes or circuits using the evaporation method andphoto-etching, it would be possible to form various electronic devicessuch as integrated circuits, light-emitting diodes, photo-diodes, andthe like on the surface of the spherical crystals. These things can alsobe done with the spherical crystals in embodiment 1 and the sphericalcrystals in embodiment 2.

Embodiment 4

(drawings omitted)

In embodiment 4, the first process involves the preparation of a crystalsubstrate comprising silicon single crystals that do not have a highdegree of purity. The substrate has a thickness of 2.0 mm and the mainsurface has a crystal orientation index of (111).

The second process through the sixth process are identical to the secondprocess through the sixth process in embodiment 1, so the descriptionswill be omitted. However, in this case what is formed are sphericalcrystals comprising silicon single crystals, and impurities aresegregated on the surface of these spherical crystals. As noted in claim1 and the section on the advantages of the invention, when the sphericalcrystal is being formed, crystal growth proceeds from the unmeltedportion of the projection (i.e. the base of the projection), andsolidification proceeds from the center of the sphere toward thesurface. This results in the impurities contained in the silicon singlecrystals being segregated to the surface of the spherical crystal.

In the seventh process following the sixth process, the surfaces of theplurality of spherical crystals are etched. The segregated impuritiesand silicon oxide films on the surfaces are removed.

If a silicon polycrystal crystal substrate is used for the crystalsubstrate, it is still possible to perform etching as described in theseventh process as described above to remove the segregated impuritiesand silicon oxide films on the surfaces.

Embodiment 5

(drawings omitted)

In embodiment 5, the first process involves preparing a crystalsubstrate comprising silicon single crystals that do not have a highdegree of purity, as in embodiment 4. The substrate has a thickness of2.0 mm and the main surface has a crystal orientation index of (111).

The second process through the sixth process are identical to the secondprocess through the sixth process in embodiment 1, so their descriptionswill be omitted. In this case, the results are spherical crystals ofsilicon single crystals, and impurities are segregated on the surfacesof the spherical crystals.

In the seventh process, as in the seventh process in embodiment 4, thesurfaces of the plurality of spherical crystals are etched to remove thesilicon oxide films and the segregated impurities.

In the eighth process, the plurality of spherical crystals, from whichimpurities were eliminated in the seventh process, are melted again by alaser beam as in the sixth process in embodiment 1. The crystalssolidify and are recrystallized. With this recrystallization, impuritiesare again segregated on the surface of the spherical crystal, so theseventh and eighth processes are repeated multiple times.

In this way, the degree of purity in each of the spherical crystals canbe improved, making it possible to provide very pure spherical siliconsingle crystals. Thus, since impurities contained in spherical crystalscan be removed, it is possible to use crystal substrates made from lesspure material, such as metallurgical-grade silicon polycrystals. Thiswould be significantly less expensive compared to crystal substratesmade from silicon single crystals. Thus, it is possible to makespherical crystal arrays at relatively low costs. As the diameter of thespherical crystals gets smaller, the crystals will tend to become singlecrystals. Also, since the ratio of surface area to volume will increase,there is a stronger impurity "getter" effect from the surface.

Embodiment 6

(no drawings)

Impurities and silicon dioxide films on the surfaces of the plurality ofspherical crystals made according to the method described in embodiment5 are etched and removed.

Next, the crystal substrate on which the spherical crystals are formedare placed in a thermal oxidation furnace as in the fourth process inembodiment 1. A silicon dioxide film (having a thickness of 1.0 microns,for example) in which there is phosphorous doping is formed on thesurfaces of the spherical crystals and on the other surfaces. Next, heatis applied, at 1000-1200 degrees C for example, to the plurality ofspherical crystals and the crystal substrate so that the impuritieswithin the spherical crystals are gettered by the oxide film. Then, thesurfaces of the spherical crystals are etched to remove the oxide filmin which the impurities have been gettered. Even by repeating theseventh and eighth processes in embodiment 5, it is still difficult tocompletely eliminate elements on which there is not much segregation andwhich have high coefficients of diffusion (e.g. Au, Ag, Cu in siliconcrystals). The processing in this embodiment makes it possible to almostcompletely remove the impurities from elements with high coefficients ofdiffusion.

The processing described in embodiment 6 can also be applied to thespherical crystals made according to the methods described inembodiments 1 through 4.

Embodiment 7

(no drawings)

In embodiment 7, annealing is performed on the spherical crystals whenthere are problems involving internal stress or crystal defects thatoccur within the crystals during growth.

First, the spherical crystal array made according to the methoddescribed in embodiment 1 is placed in a heating furnace and heated at aselected temperature, such as a temperature within the range of 700-1200degrees C. Then, the heated spherical crystal array is removed from theheating furnace and cooled to room temperature. By annealing thespherical crystal array in this manner it is possible to reduce internalstress and crystal defects. The method used in this embodiment 7 canalso be applied to the spherical crystal arrays made according to themethods in embodiments 1 through 6.

Embodiment 8

(see FIG. 18 and FIG. 19)

Referring to FIG. 8, in the first process in embodiment 8 a polycrystalsubstrate 30B having a thickness of 1.5 mm and comprising a silicon thatdoes not have a high degree of purity is used. A single crystalsubstrate 30C having a thickness of 1.0 mm, comprising a silicon singlecrystal, and having crystal orientation index of (111) is also prepared.Single crystal substrate 30C is adhered to the upper surface ofpolycrystal substrate 30B using a known thermal pressure bonding method.This results in a crystal substrate 30A.

Processes 2 through 6, which are similar to processes 2 through 6 fromembodiment 1, are performed on crystal substrate 30A to form 25spherical single crystals.

In other words, since projection 32 comprises silicon single crystals,it is possible to make spherical crystals comprising silicon singlecrystals. And, since it is possible to use an inexpensive polycrystalsubstrate 30B for all the parts in crystal substrate 30A except for theparts that form projections 32, it is possible to make a relativelyinexpensive spherical crystal array.

Embodiment 9

(see FIG. 20 and FIG. 21)

In the first process in embodiment 9, a crystal substrate 20 comprisinga silicon single crystal having a thickness of 2.0 mm is prepared, as inthe first process in embodiment 1.

Next, in the second process, 25 projections are formed in a 5-by-5matrix as in the second process in embodiment 2. However, theseprojections 32B are shorter than the projections 32 from embodiment 1,and can be, for example, approximately 0.8 mm in height. Next, the thirdprocess and the fourth process, which are similar to the third andfourth processes from embodiment 1, are performed. In the fifth process,the silicon dioxide film is partially removed, as in the fifth processfrom embodiment 1. However, in this fifth process, the silicon dioxidefilm 33 is removed over the whole outer surface of projection 32B alongits full height, as shown in FIG. 20.

Then, in this case, the silicon dioxide film 33 that remains around thebase of projection 32B forms a flow regulating film 33b. In the next,sixth process, this flow regulating film 33b regulates the flow of themolten silicon melt along the surface of crystal substrate 30. In thesixth process, which is roughly similar to the sixth process fromembodiment 1, a laser beam scan is performed. However, during thisheating and melting, solidification and crystallization take place aftereach projection 32B has melted completely. Even in this case, whenspherical crystal 34b solidifies, the surface tension of the siliconmelt and the flow regulation by the flow regulating film 33b result in aspherical crystal having a roughly spherical shape with no collapse inshape.

Having described preferred embodiments of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to those precise embodiments, and that various changesand modifications may be effected therein by one skilled in the artwithout departing from the scope or spirit of the invention as definedin the appended claims.

The following is a description of various forms of the present inventionthat can be implemented by applying the embodiments described above ormaking partial changes in the embodiments described above.

1) All of the above embodiments involved the formation of sphericalcrystals in environments having a gravity of 1G. However, it would alsobe possible to implement the present invention in environments ofzero-gravity or micro gravity for the steps after the process formelting the projections, and at least the process for solidifying themolten crystals.

In this case, gravity has almost no effect on the melt at the moltenportion, thus making the surface tension of the melt even more dominant.This permits the formation of spherical crystals that are more trulyspherical. This is especially effective in growing spherical crystalswhen the volume of the melt is large or the effect of its weight issignificant.

In normal gravity, temperature distribution in the melt can causeconvection and agitate the melt. Also, the use of elements withdifferent specific gravities in compounds and mixed crystals can lead tolocalized non-uniformities. These problems do not occur in micro gravityconditions.

2) There are cases where it would be desirable to use an inert gasatmosphere, such as argon, helium or nitrogen, according to the materialto be melted. This would be done in at least the process for melting andthe process for crystallizing and solidifying.

If the material to be melted is, for example, arsenic, which is anelement in the crystallization of gallium arsenide, there would be ahigh equilibrium vapor pressure and it would be possible for thematerial to decompose and evaporate during melting. In such cases, itwould be desirable grow the spherical crystals in the inert gassesmentioned above at a high gas pressure setting. It would also bepossible to set the inert gas atmosphere temperature so that the heatdissipation from the melt surface is decreased.

3) In the atmosphere used in the embodiments described above, it wouldalso be possible to introduce impurities for doping into the sphericalcrystals by using an atmosphere containing the impurities for doping.This would be done for the process for melting the projections and theprocess for crystallizing and solidifying.

4) Instead of using the carbon dioxide gas laser described in theembodiments above, it would also be possible to use YAG lasers andQ-switched ruby lasers. It would be possible to use lasers withdifferent wavelengths corresponding to the type of material to bemelted, and the spherical crystals can be formed by melting at least aportion of the projection or the entire projection.

Furthermore, instead of the laser described above, it would be possibleto melt the material by using an infrared beam focussed narrowly with acondensing lens. Also, a narrowly focused electron beam can be usedinstead of a laser or an infrared beam in order to melt and solidify ina vacuum atmosphere. Furthermore, instead of a narrowly focussed heatingbeam, it would not be impossible to have a heating beam having aprescribed width heat and melt multiple rows by scanning or withoutscanning.

5) The crystal substrate described above does not necessarily need to beformed in a plate shape, and can also be formed as a rod or in a bulk.Also, the projections described above do not necessarily need to beformed as square columns, and can be formed as circular columns as well.If circular columns can be formed economically, it would be desirable touse circular columns, since projections that are shaped as circularcolumns can form spherical crystals that are more perfectly spherical.

6) In the embodiments described above, the projections are formedintegrally on the crystal base (crystal substrate). However, it would bepossible to not form the projections integrally with the crystal baseand to make the projections separately from metal or metal oxide ornon-metallic crystals or from semiconductor single crystals. Theprojection can then be adhered or bonded to the surface of a crystalbase that is a metal, a metal oxide or a non-metallic material. It wouldalso be possible to melt, crystallize and solidify at least a portion ofthe projection, the entire projection, or the entire projection and aportion of the crystal substrate. In these cases it would also benecessary to have the configuration be able to absorb heat reliably fromthe projections to the crystal substrate.

7) For the crystal substrate and the projections formed integrally withthe crystal substrate or the projections adhered or bonded to thecrystal substrates, it would be possible to use silicon single crystals,silicon single crystals or polycrystals that do not have a high degreeof purity, or germanium single crystals or polycrystals that do not havea high degree of purity, or other various types of semiconductors,dielectrics, magnetic bodies or superconductors.

The following are examples of materials that can be used for formingspherical crystals according to the method of the present invention.

    ______________________________________                                        a) Metal oxide single crystals                                                Nd.sub.3 Ga.sub.5 O.sub.2                                                     LiTaO.sub.3       Dielectric crystal, pyroelectric                            material                                                                      LiNbO.sub.3       Same as above                                               PbTiO.sub.3       Same as above                                               GGG (Gd.sub.3 Ga.sub.5 O.sub.12)                                                                magnetochemical                                             crystal                                                                       YAG (Y.sub.3 Al.sub.5 O.sub.12)                                                                 optical crystal for use in lasers                           (dope with Nd.sup.3-)                                                         Al.sub.2 O.sub.3  Same as above (dope with Cr.sup.3+)                         b) Compound semiconductor crystals                                            GaAs, GaP, InAs, InSb, GaSb, InP                                                                III-V group                                                 ZnS, ZnSe, CdTe   II-VI group                                                 SiC               IV--IV group                                                c) mixed crystalline semiconductors                                           Si.sub.x Ge.sub.1-x                                                                             IV--IV group                                                AlGa.sub.1-x P    III-V group                                                 AlGa.sub.1-x As   III-V group                                                 AlGa.sub.1-x Sb   III-V group                                                 Ga.sub.x In.sub.1-x P                                                                           III-V group                                                 Ga.sub.x In.sub.1-x Sb                                                                          III-V group                                                 Ga.sub.x In.sub.1-x As.sub.y P.sub.1-y                                                          III-V group                                                 ZnS.sub.x Se.sub.1-x                                                                            II-VI group                                                 Cd.sub.1-x Zn.sub.x Te                                                                          II-VI group                                                 Hg.sub.1-x Cd.sub.x Se                                                                          II-VI group                                                 Pb.sub.1-x Sn.sub.x Te                                                                          IV-VI group                                                 Pb.sub.1-x Sn.sub.x Se                                                                          IV-VI group                                                 ______________________________________                                    

8) For the crystal base described above, it would be possible to use:metallic single crystals, intermetallic compound crystals andpolycrystals; metal oxide single crystals, mixed metal oxide singlecrystals and polycrystals; non-metallic single crystals, mixednon-metallic single crystals and polycrystals; or various combinationsof these materials.

The projections formed integrally with or separate from the crystal basecan comprise: metallic single crystals, intermetallic compound singlecrystals and polycrystals; metal oxide single crystals, mixed metaloxide single crystals and polycrystals; non-metallic single crystals,mixed non-metallic single crystals and polycrystals; or variouscombinations of these materials. Spherical crystal arrays using metal ormetal oxide can be used industrially as a discharge electrode unitcontaining a plurality of discharge electrodes.

9) The spherical crystal arrays described above can be processed withvapor phase growth, vapor phase diffusion, oxide film formation,electrode formation and the like so that each spherical crystal in thespherical crystal array can form a photodiode. This will result in agood optical sensing element that can detect light coming in fromvarious directions.

10) In the above embodiment, the projections are supported pointingdownward while melting and solidification take place. However, it is notimpossible for melting and solidification to take place while theprojections are pointing upward.

11) Referring to FIG. 22, instead of the projections in the embodimentabove, it would also be possible to form a pair of projections 71projecting integrally from crystal substrate 70 so that they are facingeach other. A heating beam would be applied to the tips of projections71 so that they are melted and then solidified, thus forming sphericalcrystals 72 on the tips of projections 71. In this case, flow regulatingfilm is formed as in the embodiments above.

12) In the above embodiments, the projections are positioned on thebottom side of the crystal base, and the laser is applied from thebottom of the projections to the tip of the projections. However, itwould also be possible to position the projections on the top side ofthe crystal base and have the laser applied from above to the tip of theprojections.

13) The spherical crystals formed according to the methods described inthe above embodiment can be made separately from the crystal substrateafter integrated circuits, electrodes and terminals are installed, orbefore they are installed. They can then be used as electronic devices,optical elements, functional electronic elements and the like.

14) The spherical crystals described above is formed using a heatingbeam. Depending on the application, the heating beam can be a pluralityof lasers having the same wavelength, or a plurality of lasers havingdifferent wavelengths, or a plurality of condensed infrared beams, or acombination of these.

15) Besides using a diamond multi-blade saw or ultrasonic processing,the projections can be formed on the crystal substrate using chemicaletching, sand blasting, vapor phase epitaxial growth, or the like.

16) Regarding the flow regulating film, it would be desirable for thefilm to comprise a passivation film that has a melting point that ishigher than the material to be grown as a crystal, that has a lowwettability relative to the material to be grown as a crystal, thatreacts chemically with the melt, and that does not thermally decomposeat high temperatures. If the material to be grown as a crystal issilicon, then silicon dioxide film, silicon nitride film, aluminum oxidefilm and the like can be used in the flow regulating film. If thematerial to be grown as a crystal is gallium arsenide, indium,phosphide, or the like, then silicon oxide film, silicon nitride film,aluminum oxide film and the like can also be used in the flow regulatingfilm. Also, in this case the flow regulating film can be formed usingchemical vapor phase growth (CVD).

What is claimed is:
 1. A method for making spherical crystalscomprising:forming at least one thin projection, wherein said projectioncomprising a crystal made from a member of the group consisting of ametal, a metal oxide, and a non-metallic material projects from asurface of a crystal base comprising a member of the group consisting ofa metal, a metal oxide, and a non-metallic material; forming a flowregulating film, having a higher melting point than the melting point ofsaid crystal of said projection, over said surface of said crystal baseexcluding an area proximate to a tip of said projection; applying aheating beam to said tip of said projection effective to melt a portionof said projection exposed past said flow regulating film toward saidtip to form a molten portion; and halting application of said heatingbeam on said projection so that said molten portion is solidified into aspherical crystal having substantially a spherical shape.
 2. A methodfor making spherical crystals according to claim 1 wherein:at least saidfourth process is performed in zero gravity or microgravity.
 3. A methodfor making spherical crystals according to claim 1 further comprising:afifth process, wherein a second surface of said solidified sphericalcrystal is etched to remove impurities accumulated on said secondsurface of said spherical crystal.
 4. A method for making sphericalcrystals as described in claim 1 further comprising the following twosteps performed at least once:a fifth process, wherein a second surfaceof said solidified spherical crystal is etched to remove impuritiesaccumulated on said second surface of said spherical crystal; and asixth process, wherein said spherical crystal, from which impuritieswere removed in said fifth process, is melted again and solidifiedeffective to recrystallize said spherical crystal in a substantiallyspherical shape.
 5. A method for making spherical crystals as describedin claim 4 wherein:after said sixth process, a first oxide film on saidsecond surface of said solidified spherical crystal is removed, a secondoxide film is formed on said surface of spherical crystal; and heat isapplied to said solidified spherical crystal effective to causeabsorption of impurities in said solidified spherical crystal by saidsecond oxide film.
 6. A method for making spherical crystals asdescribed in claim 1 wherein:annealing is performed on said solidifiedspherical crystal in order to decrease internal stress and latticedefects in said solidified spherical crystal.
 7. A method for makingspherical crystals as described in claim 1 wherein:a first oxide film isremoved from a second surface of said solidified spherical crystal; asecond oxide film is formed on said second surface of said solidifiedspherical crystal; and heat is applied to said solidified sphericalcrystal effective to cause said second oxide film to absorb impuritiesfrom said solidified spherical crystal.
 8. A method for making sphericalcrystals comprising the steps of:a first process, wherein one or morethin projections are formed so that they project integrally from asemiconductor crystal base; a second process, wherein a flow regulatingfilm having a higher melting point than the melting point of saidsemiconductor is formed over an entire outer surface of a base portion,excluding a portion of said outer surface proximate to a tip of saidprojection; a third process, wherein a heating beam is applied to saidtip of said projection to melt a portion of said projection past saidflow regulating film toward said tip to form a molten portion; and afourth process, wherein the application of said heating beam on saidprojection is halted, and said molten portion is solidified into aspherical crystal having substantially a spherical shape.
 9. A methodfor making spherical crystals as described in claim 8, wherein:saidsemiconductor crystal base is a semiconductor polycrystal base that doesnot have a high degree of purity.
 10. A method for making sphericalcrystals according to claim 8, wherein:a semiconductor single crystal isused for said semiconductor crystal base.
 11. A method for makingspherical crystals comprising the steps of:a first process, wherein oneor more thin projections comprising a semiconductor crystal are formedso that they project from a semiconductor crystal base; a secondprocess, wherein a flow regulating film having a higher melting pointthan the melting point of said semiconductor of said projection isformed over an outer surface of a base portion, excluding a portion ofsaid outer surface proximate to a tip of said projection; a thirdprocess, wherein a heating beam is applied to said tip of saidprojection to melt a portion of said projection past said flowregulating film toward said tip to form a molten portion; and a fourthprocess, wherein the application of said heating beam on said projectionis halted, and said molten portion is solidified into a sphericalcrystal having substantially a spherical shape.
 12. A method for makingspherical crystals according to claim 11 wherein:a semiconductor singlecrystal is used for said semiconductor projection.
 13. A method formaking spherical crystals comprising the steps of:a first process,wherein one or more thin projections comprising a crystal made from ametal or a metal oxide or a non-metallic material are formed so thatthey project from a surface of a crystal base comprising a metal or ametal oxide or a non-metallic material; a second process, wherein a flowregulating film having a higher melting point than the melting point ofsaid crystal of said projection is formed on said surface of saidcrystal base; a third process, wherein a heating beam is applied to atip of said projection to melt the entirety of said projection to form amolten portion; and a fourth process, wherein the application of saidheating beam on said projection is halted, and said molten portion issolidified into a spherical crystal having a substantially sphericalshape.
 14. A method for making spherical crystals comprising:a firstprocess, wherein one or more thin projections are formed so that theyproject integrally from a surface of a semiconductor crystal base; asecond process, wherein a flow regulating film having a higher meltingpoint than the melting point of said semiconductor is formed on saidsurface of said semiconductor crystal base; a third process, wherein aheating beam is applied to a tip of said projection to melt the entiretyof said projection to form a molten portion; and a fourth process,wherein the application of said heating beam on said projection ishalted, and said molten portion is solidified into a spherical crystalhaving a substantially spherical shape.
 15. A method for makingspherical crystals comprising:a first process, wherein at least one thinprojections made from semiconductor crystals are formed so that theyproject from a surface of a semiconductor crystal base; a secondprocess, wherein a flow regulating film having a higher melting pointthan the melting point of said semiconductor of said projection isformed on said surface of said semiconductor crystal base; a thirdprocess, wherein a heating beam is applied to a tip of said projectionto melt an entirety of said projection to form a molten portion; and afourth process, wherein the application of said heating beam on saidprojection is halted, and said molten portion is solidified into aspherical crystal having a substantially spherical shape.